O. M. Poltorak*, E. S. Chukhray, and I. Y. Torshin

Received September 2, 1997
Results of kinetic studies on dissociative thermal inactivation of
oligomeric enzymes are discussed. Dissociative thermal inactivation is
the process in which the kinetically irreversible protein change is
preceded by a reversible stage of oligomer dissociation. In
experiments, this is demonstrated by the dependence of inactivation
rate on total protein concentration. This paper gives the relations
which allow the calculation from experimental data the following
physicochemical constants which characterize the stability of
oligomeric enzymes: the constant for the rate of irreversible change of
monomeric protein, the equilibrium constant for dimer dissociation, and
the rate constant for dimer dissociation. The problem of a
"conformational lock", the contact between protein globules
that admits a multistep destruction of active oligomer and explains the
induction period occurring in kinetic thermal inactivation curves, is
discussed. The X-ray structural analyses for such dimeric enzymes as
alkaline phosphatase (EC 3.1.3.1) from E. coli, alcohol
dehydrogenase (EC 1.1.1.1) from horse liver, and bakers yeast
enolase (EC 4.2.1.11) explain why they lose catalytic activity during
the dissociation of the protein into monomers and also provide a
physically reasonable picture of the structure of their conformational
lock. Also, these data have made a basis for the kinetic scheme used to
describe the dissociative inactivation of dimeric enzymes.
KEY WORDS: oligomer, dimer, monomer, conformational lock,
dissociative thermal inactivation, stability